This paper describes a new method to prepare polyethylene graft copolymers, such as polyethylene-g-polystyrene and polyethylene-g-poly(p-methylstyrene), with a relatively well-controlled reaction mechanism. The chemistry involves a transformation process from the metallocene copolymerization of ethylene and p-methylstyrene to the anionic living polymerization of styrene or p-methylstyrene. The metallocene catalysis produces poly(ethylene-co-p-methylstyrene) random copolymers with molecular weight distribution (M̄ w/M̄ n) of about 2.5. The following selective metalation reaction of p-methylstyrene units in the copolymer and the subsequent anionic “living” graft-from polymerization were effective to produce polymeric side chains with well-defined structure. Both graft density and graft length can be controlled by p-methylstyrene content in the PE backbone, metalation reagent, and the quantity of monomer used in the graft-from reaction. In the bulk, the individual PE and PS segments in the graft copolymers are phases-seperated to form crystalline PE domains and amorphous PS domains. The microscopy studies reveal the effectiveness of PE-g-PS in the polymer blends by reducing the phase sizes, improving the dispersion, and increasing interfacial interaction between domains.

Monoalkyl-and dialkyl-imidazolium surfactants were used to prepare organically modified montmorillonites with markedly improved thermal stability in comparison with their alkyl-ammonium equivalents (the decomposition temperatures increased by ca. 100°C). Such an increase in the thermal stability affords the opportunity to form syndiotactic polystyrene (s-PS)/imidazolium-montmorillonite nanocomposites even under static melt-intercalation conditions in the absence of high shear rates or solvents. Upon nanocomposite formation, s-PS exhibited an improvement in the thermal stability in comparison with neat s-PS, and the ␤-crystal form of s-PS became dominant. This crystallization response agrees with previous studies of s-PS/pyridinium-montmorillonite hybrids and is tentatively attributed to a heterogeneous nucleation action by the inorganic fillers.

A family of cross-linked polypropylene (x-PP) thin film dielectrics is systematically studied to understand the cross-linking effect on the dielectric properties. Evidently, the butylstyrene (BSt) cross-linkers increase both the dielectric constant (ε) and breakdown strength (E), without increasing energy loss. An x-PP dielectric, with 3.65 mol % BSt cross-linkers, exhibits a ε∼3, which is independent of a wide range of temperatures and frequencies, slim D-E hysteresis loops, high breakdown strength (E=650 MV/m), narrow breakdown distribution, and reliable energy storage capacity >5 J/cm3 (double that of state-of-the-art biaxially oriented polypropylene capacitors), without showing any increase in energy loss.

We use simulations and experiments to delineate the mechanism by which the addition of a small number of polar −OH groups to a nonpolar polymer increases the static relative permittivity (or dielectric constant) by a factor of 2, but more importantly while keeping the dielectric loss in the frequency regime of interest to power electronics to less than 1%. Dielectric properties obtained from experiments on functionalized polyethylenes and polypropylenes as a function of −OH doping are in quantitative agreement with one another. Molecular dynamics simulations for the static relative permittivity of “dry” −OH functionalized polyethylene (in the absence of water) are apparently in quantitative agreement with experiments. However, these simulation results would further imply that there should be considerable dielectric loss beyond simulation time scales (>0.1 μs). Since there are minimal experimentally observed dielectric losses for times as short as a microsecond, we believe that a small amount of adsorbed water plays a critical role in this attenuated loss. We use simulations to derive the water concentration at saturation, and our results for this quantity are also in good agreement with experiments. Simulations of the static relative permittivity of PE–OH incorporating this quantity of hydration water are found to be in quantitative agreement with experiments when it is assumed that all the dipolar relaxations occur at time scales faster than 0.1 μs. These results suggest that improved polymeric dielectric materials can be designed by including −OH groups on the chain, but the mechanism requires the presence of a stoichiometric quantity of hydration water.

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Summary: Copolymerization of propylene and 1,4‐divinylbenzene was successfully performed by a MgCl2‐supported TiCl4 catalyst, yielding isotactic poly(propylene) (i‐PP) polymers containing a few pendant styrene groups. With a metalation reaction with butyllithium and a hydrochlorination reaction with dry hydrogen chloride, the pendant styrene groups were quantitatively transformed into benzyllithium and 1‐chloroethylbenzene groups, respectively, which allowed the synthesis of i‐PP‐based graft copolymers by living anionic and atom transfer radical (ATRP) polymerization mechanisms.The incorporation of styrene pendant groups into isotactic poly(propylene) using a Zeigler–Natta catalyst gave functionalized polymers able to undergo living anionic and atom transfer radical (ATRP) polymerizations.imageThe incorporation of styrene pendant groups into isotactic poly(propylene) using a Zeigler–Natta catalyst gave functionalized polymers able to undergo living anionic and atom transfer radical (ATRP) polymerizations.

This article discusses a new method to prepare polypropylene membrane that has hydrophilic surfaces and asymmetric porous structure. This membrane is based on a newly developed hydroxylated polypropylene (PP-OH), which has a ''brushlike'' microstructure, high molecular weight, high melting point, and relatively high concentration of hydroxy groups. Under the leaching process conditions, various asymmetric hydrophilic PP/PP-OH membranes are prepared with controllable pore structures. The PP-OH polymer becomes the surface modifier of asymmetric PP membrane with flexible functional groups located on the membrane surfaces, including pore surfaces. This new hydrophilic PP/PP-OH membrane is useful in ultrafiltration, not only offering good selectivity and flux but also showing excellence in antifouling property.

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